A one-dimensional approach towards edge crack detection and mapping using eddy current thermography

Abstract

Eddy current thermography (ECT) is an emerging nondestructive evaluation (NDE) technique, which is used to detect defects in metallic components. In this study, a one-dimensional (1D) heat transfer approximation is delivered to detect, locate and size surface edge cracks in bar samples using a low-power ECT experimental setup. The induction of eddy current heat generation function on one side of the sample delivers a quasi-one-dimensional heat transfer model where heat only propagates along the sample. The presented model takes into consideration convection heat transfer losses along the sample. It is demonstrated that convection heat transfer losses are considered negligible as heat propagates along a relatively high thermal conductivity metallic material such as aluminum alloys. This leads to an approximately uniform temperature gradient in a quasi-steady-state heat transfer condition along a crack-free sample. The presence of an edge crack alters the heat propagation near the crack. Accordingly, estimating the temperature gradient along a sample at a quasi-steady-state condition allows the detection and sizing of edge cracks far from the ECT excitation coil. Applying the proposed ECT inspection technique to detect edge cracks in aluminum alloys delivered an accuracy of 13 % in crack depth estimation.